Since Drs Chu Ching-wu and Wu Mao-kun have successfully obtained materials having superconductive properties at a critical temperature of about 90 K from oxides of yttrium, barium, and copper in February 1987, numerous efforts all over the world have contributed to research in the field, and superconductors have become the focus in scientific and technological fields. Thereafter, oxides of bismuth, (lead), strontium, calcium, copper having critical temperatures of 80 to 110 K, followed by new superconductive materials--oxides of thallium, barium, calcium, copper--having critical temperatures of as high as 120 K have been disclosed one after another.
Since the superconductors have a resistance of zero and are capable of internally eliminating the magnetic field in response thereto, and thus resulting in magnetic levitation, they have potentially widespread applications. Among others, superconductive films play a rather important role in the electronics field. That is, the particular phenomenon of superconduction, or the "Josephson effect", can be used for making "Josephson devices" and "superconductive quantum interference devices" (SQUID), which will lead to unmeasurable innovations in modern electronics.
In general, superconducting films are made by means of either "evaporating" or "sputtering" methods, and the latter is more widely used. Briefly, in the so-called "sputtering" method, gas ions are used to bomb a target such that the splashed molecules of the material are sprayed onto a substrate to form into a film. To make films by means of "sputtering", however, there exists an important technical problem, that is, the making of the "sputtering target", which relates to the difficulty involved in sputtering the superconductor films and the quality thereof.
For example, the formation, compositions, uniformity, compactness, surface smoothness are all important factors which affect the sputtering and quality of the superconductor films. Therefore, how to make ideal superconductor sputtering targets is presently the most important subject.